Exhaust Gas Recirculation (EGR) systems may be provided in vehicles for the purpose of reducing nitrogen oxides (NOx) contained in exhaust gas discharged from the combustion chambers of internal combustion engines. A portion of the exhaust gas discharged from the combustion chambers may be recirculated through an exhaust recirculation passage to an intake passage and back to the engine cylinders. The recirculation of the exhaust gas may inhibit the formation of NOx by mixing with the air-fuel mixture in the engine cylinders to lower the combustion temperature.
However, as the combustibility of the air-fuel mixture in the combustion chamber decreases with the presence of the recirculated exhaust gas, there may be a corresponding decrease in engine output and engine operability. Hence, it may be necessary to regulate the flow rate of the recirculated exhaust gas to the intake passage according to the operation of the engine. An EGR valve may be provided in the EGR system to control and time the flow of the recirculated exhaust gas.
During operation of an engine the EGR valve may malfunction and fail in a single position, due to any number of causes. Such failure may incapacitate the valve to regulate the flow of recirculated exhaust gas leading to engine problems.
If the EGR valve malfunctions and fails in a fully open state, an excessive amount of the recirculated exhaust gas may be supplied to the engine which may affect a combustion state of the engine. Thus, the engine operation may be destabilized.
WO2009127929 discloses an internal combustion engine with separate cylinder banks Separate exhaust passages may be connected to each cylinder bank. A shared intake passage may be connected to both cylinder banks, with an end of the EGR passage being connected to the exhaust passage of one cylinder bank, and the other end of the EGR passage being connected to the shared intake passage. If it is determined that an EGR valve in the EGR passage is stuck in an open state, a fuel-cut control may be executed in that cylinder bank that is connected to the separate exhaust passage to which the EGR passage is connected. Thus, even when the EGR valve fails in an open state, it may possible to prevent the internal combustion engine from operating unstably.
U.S. Pat. No. 4,378,776 discloses means for closing a recirculation passage for preventing excessive amount of exhaust gas recirculation. A device may be provided for closing the EGR valve when the actual valve position does not conform with the desired position for a predetermined time. A spring may be provided which forces the EGR valve to the closed position.
However, EGR valves which fail in the fully closed position may result in related problems such as turbo overspeed and NOx non compliance. The present disclosure is directed, at least in part, to improving or overcoming one or more aspects of the prior art EGR valves.